Things like the Lenovo M93p mini PC are a great platform, and a good way to help recycle (re-use) old corporate purchases.

AMD is preferable to Intel for the highest quality Linux video support (tear-free 4k.) If your ambient environment and workload can handle it you can take the fan out and have them passively cool themselves too.

Here is a good resource for reviews of for these types of machine:

https://www.servethehome.com/tag/tinyminimicro/

Secondhand HP T620 is pretty cheap and comes with sodimm and m2 sockets. T610 has weaker processor and sata instead of m2, but much cheaper than T620. I'm running homeassistant and pihole in a T610 with 8gb ram and 256 ssd and it's pretty great so far.

Lenovo M600 Tiny. It's nuclear bomb proof, runs on virtually no watts, has no fan and runs headless linux fine. Also supports proper storage like M2 SATA disks and doesn't have the horrible power supply issues you tend to get from Pi's. Usually available relatively cheaply on eBay.

I was running a cluster of 4 of them when I was learning about Kubernetes

Spec sheet: https://psref.lenovo.com/syspool/Sys/PDF/ThinkCentre/ThinkCe...

One example would be the Gigabyte Brix line. These barebones start at around 70€ and you get a 4W Celeron 2C/2T, USB3, GB Lan, WiFi, VGA and HDMI output. You need to add RAM to the bill but you could easily find a matching 4 GB DDR4 stick for under 15€. You also need storage but thats also needed for the Pi. So you're starting at 85€ with this mini-pc. Still you need to figure out if it matches your application needs, like if you need to interface with hw via GPIOs etc.

got a Fujitsu S740 for about 40USD (used, 2.5 y.o.). It's a thinclient (similar to the T620 below) and as such sadly doesn't have Wifi-onboard (but 1 SATA M.2 and 1 E-Key inside). Otherwise beats any SBC by an order of magnitude probably. The board inside is actually sold as a "SBC" by Kontron as well...

If you are fine with older stuff and adapt a PSU, you can probably get RPI-performance (even GPIO in a real parallel-port!) for the price of a coffee.

Sadly, the alternatives in that price range aren't all that great. Mostly celerons or Arm SoC with bad to horrible software support.

I really liked my pi 3b+ but it died on me and I just can't justify the price of 4b. I've been looking at 5800u mini pcs but 500 euro for a barebone that will only serve a few local web apps doesn't sit well with me. It would be such a massive waste.

I've been in that limbo for more than an year. Where's that pi 5 :(

I've had great success with Orange Pi boards, just check Armbian support before buying, otherwise you're stuck with their outdated Ubuntu images. The prices have gone up as well, but not even remotely as much as RPi.

The Nano pi line from friendlyarm has been solid for me. They're well built vs the jank that OrangePi tends to ship.

Pine64 sells pretty good boards as well, though I'd place them a half step below the quality of friendlyarm.

ODROID-H3 or ODROID-H3+. Know nothing about them other than that they exist...

I'm happy with my Quartz64.